This disclosure relates to a fiber reinforced polymeric material overmolded onto a polymeric insert to form a closed section geometry for use as a structural reinforcement component, and methods of making the same. In particular, disclosed herein is a closed section reinforcement structure for use in a structural component of a vehicle such as a lift gate and methods of making the same.
Structural components for vehicles, such as front end modules and lift gates, can be loaded with torsion due to forces acting at separate locations. To accommodate this requirement, having high bending stiffness in such structural components is desirable. A lift gate is a large component member of a vehicle body, and rotates significantly around a hinge when it opens or closes. Lift gates are provided to open or close an opening portion formed at a rear portion of a hatch back type of passenger vehicle or the like. Due to the level of stress from the repeated opening and closing of the lift gate and the size of the lift gate, ribs or steel inserts can be employed to ensure proper operation and structural stability. Other attempts to increase the stiffness and torsional rigidity include increasing the thickness of the panels. However, an increase of the panel thickness and/or the addition of the ribs for increasing the rigidity of the lift gate also increases the overall weight of the lift gate, which can negatively affect the fuel efficiency of the vehicle. Furthermore, the use of reinforcements, such as ribs, can affect the ability to efficiently run wires, cables, or the like through the lift gate. In addition, ribs and other reinforcements negatively impact the aesthetic quality of the lift gate because such features can leave visible imperfections on the panels, thus requiring an additional panel to be installed to provide a finished appearance. The use of steel or other materials in combination with a plastic lift gate can also add manufacturing time and expense to the production of a lift gate or vehicle component.
Because the weight of a vehicle body has an impact on the fuel consumption of the vehicle, attempts have been made to produce a lift gate from lighter-weight materials, such as polymeric materials, in an effort to reduce the overall weight of the vehicle. The use of polymeric materials reduces the overall weight, but in some applications may not accommodate stresses and strains placed on the lift gate. As an example, the lift gate may bend undesirably. This can displease a consumer. Worse yet, such flexure may fail to sufficiently resist deformation in a crash.
For some applications, techniques such as injection molding and/or injection compression molding, such as with a given drawn direction and sliders, cannot provide desired and/or sufficient torsion stiffness for a structural component. Other techniques, such as gas injection molding and water injection molding, do not provide the requisite control over wall thicknesses. In addition, the use collapsible cores and sliders can include parts that shift during a molding process resulting in deviations in the intended wall thickness. Thus, attempts have been made using metal inserts to provide a surface for molding a polymeric structural component. However, metal inserts add weight and negatively impact the fuel economy of a vehicle. Moreover, past attempts to manufacture fiber reinforced components exhibit numerous manufacturing defects including varying wall thickness and difficulty in reproducing wall thicknesses. For example, long glass fiber reinforced plastics can suffer from “fiber foaming” at the inside of the component (e.g., where the fiber reinforced plastic contacts a load bearing slider, core, or metallic insert).
Accordingly, a need exists for light-weight polymeric components including fiber reinforced polymers with controllable, reproducible wall thicknesses.